Low light solutions

The right amount of light

Shutter speed is an important factor for capturing good images. The shutter opens for a brief period, allowing enough light to reach the sensor. It then closes again to prevent the image from being overexposed. In bright daylight the shutter only needs to be open for a few milliseconds, but as the light level drops, it needs to stay open longer. At some point this will cause motion blur if there is movement in the scene.

So, a fixed scenario might look good in low light with slow shutter speeds, although anything moving in the scene will become blurred and potentially unidentifiable.

Figure 4: Motion blur is caused by movement in the scene combined with a slow shutter speed.

The lens also affects the low-light performance of a camera. A lens with high quality glass elements and a wide aperture lets in more light and allows faster shutter speeds.

When comparing different camera models for low-light situations, be sure they are fitted with a suitable lens. A lower f-stop value means the lens has a wider maximum aperture and will perform better in low light. Some cameras automatically adjust the aperture (also known as the iris) depending on the available light in the scene, making these models suitable for scenarios where the amount of light varies.

Figure 5: The size of the aperture affects the image quality. A large aperture means a low F-stop value. A small aperture means a high f-stop value.

The difference in intensity between the brightest and darkest parts of a scene is called the dynamic range. When this range extends beyond the capabilities of the image sensor, some parts of the image will be rendered without any detail, just all white or all black.

A camera with Wide Dynamic Range capabilities is designed to function better in environments with large variations in light intensity. Be sure to test the camera in its intended environment.

Figure 6: The first two images show how the wide dynamic range in the monitored scene causes parts of the image to be overexposed or underexposed. In the image to the right, WDR dynamic capture has been used, resulting in a balanced image with all areas visible.